Thanks for all the help and advice. I think I'll go with AA as they're the only airline that seem to service all the routes I'm likely to fly (with reasonable times). UA was definitely better for Maui but with the latest news about AA and BA (I know it will take time if indeed it happens at all) I think AA are the best option for me.

I'll be PremEx again on UA this year but do you think AA will match that if I switch to flying with them all the time? I know BA matched another airline for a colleague of mine but I have never tried this myself.